SCWO characteristics are investigated for a vertical type, down stream continuous reactor system with mixing nozzle and sapphire windows. 2-propanol, hexane and biphenyl solution are used as fuel and air as oxidizer. 2-propanol is observed to be effective as makeup fuel to keep a stable autogenic SCWO reaction. Even for low air ratio as 1.1, high decomposition rate without CO, NO, NO2 or soot production is achieved. Calculated and experimental flue gas composition is in good agreement for a wide range of air ratio. Spontaneous flame formation is observed for SCWO of 2-propanol using air ratio over 1.8. These flame formations are not particular to 2-propanol and are also confirmed when using hexane and biphenyl solution as fuel.